This invention relates to a process for etching a multi-layer substrate, and more particularly to a process for effectively and efficiently etching multi-layer devices such as semiconductor devices.
It is known in the prior art that the manufacture of multi-layer semiconductor devices typically involves patterned etching using liquid or wet etching materials, or dry etching with halogens or halogen-containing compounds, of certain layers which comprise features these devices. For example, one well known etching material is chlorine which can exist in the etching process as either chlorine gas or HCl, etc. Chlorine etches the semiconductor isotropically, i.e., in both a lateral and vertical direction. This results in an etched feature which has a line width which is smaller than the resist image.
Etching can also be conducted in a gas phase using known techniques such as plasma etching, ion beam etching, and reactive ion etching. The gas plasma technology employs gaseous ions, typically generated by an RF discharge for etching and removing the requisite portion of the surface to be etched using a chemical reaction between the gaseous ions and the subject surface. In the anisotropic process, etching takes place only or primarily in the vertical direction so that feature widths substantially match the photoresist pattern widths. In U.S. Pat. No. 4,734,157 an elemental silicon-containing layer, such as a layer of polysilicon or silicide, is etched anisotropically employing a gas plasma comprising a gaseous chlorofluorocarbon, capable of supplying CF.sub.x and chlorine ions, and ammonia. Profile control of a silicon layer is controlled by the use of this etching mode.
The prior art etching chemical systems typically employ a mixture of etching chemicals. One portion of the mixture forms a fluorocarbon polymer, other portions provide additives for controlling bias or other application specifications, and another is an inert carrier material. The above-described prior art systems include CHF.sub.3 /CF.sub.4 /He, CHF.sub.3 /SF.sub.6 /Ar, C2F.sub.4 /CF.sub.4 /Ar, and C.sub.2 F.sub.6 /NH.sub.3 /Ar.
In the etching process, a chemical etchant protective patterned layer is first formed on a major surface of the semiconductor device, typically on the outer surface of that device. Then, a chemical etchant protective patterned layer is provided and a predetermined pattern of openings are formed in the chemical etchant protective patterned layer based on a desired etch pattern. This exposes a plurality of areas of the major surface of the semiconductor device corresponding to a predetermined pattern of openings. Once the chemical etchant protective patterned layer is in place, the etching operation can commence.
An important aspect in forming a multi-layer semiconductor device, including a structural layer of SiO.sub.2 formed on a silicon substrate, is controlling the selectivity of SiO.sub.2 to Si or metal silicide ratios, particularly if a halogenated plasma gas is employed in a plasma etchant work area. The above-described fluorocarbon etchant gaseous mixtures are useful for that purpose. However, in each case where a multiple bond fluorocarbon, a hydrogen-containing fluorocarbon, a fluorocarbon and hydrogen, or a mixture of gases which include a carbon-containing gas, a hydrogen-containing gas and a halogen-containing gas are present in the plasma etch material, a fluorocarbon polymeric material is indiscriminately deposited on all of the surfaces of all of the production equipment located within the plasma etchant work area (see FIG. 1). The effect of this non-localized polyfluorocarbon deposition is the following:
1. a limiting condition for controlling the selectivity of SiO.sub.2 to Si or metal silicide due to excessive polymer formation in the reactor when high SiO.sub.2 to Si or metal silicide selectivities are obtained;
2. processes which are unstable due to excess polyfluorocarbon material builds-up; and
3. a requirement for more frequent cleaning of the equipment which results in a relatively high level of production downtime.
Therefore, a need exists for a process for etching semiconductor devices which selectively controls the SiO.sub.2 to Si or metal silicide ratio, which is stable and avoids undue polymer build-up, and which requires only limited cleaning of the equipment.